Optics: eye examining – vision testing and correcting – Spectacles and eyeglasses – Ophthalmic lenses or blanks
Reexamination Certificate
2002-10-25
2003-12-30
Sugarman, Scott J. (Department: 2873)
Optics: eye examining, vision testing and correcting
Spectacles and eyeglasses
Ophthalmic lenses or blanks
Reexamination Certificate
active
06669337
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a progressive spectacle lens as set out in the preamble of patent claim 1, the lens having low swaying effects.
Progressive spectacle lenses (also called varifocal lenses, multifocal lenses etc.) are usually understood to be spectacle lenses having a different (lower) power in the region through which a spectacles wearer views an object located at a great distance—hereunder referred to as a distance portion—than in the region (near portion) through which the spectacles wearer views a near object. Located between the distance portion and the near portion is the so-called progressive zone in which the power of the spectacle lens continuously increases from that of the distance portion to that of the near portion. The magnitude of the power increase is also designated as addition power.
As a rule, the distance portion is located in the upper part of the spectacle lens and designed for viewing “to infinity”, whilst the near portion is located in the lower region and is particularly designed for reading. In spectacles for special application—those for pilots or for monitor work stations are mentioned as examples—the distance and near portions may also be arranged differently and/or designed for other distances. Furthermore, it is possible for a plurality of near portions and/or distance portions and suitable progressive zones to be present.
With progressive spectacle lenses having a constant refractive index it is necessary, in order that the power may increase between the distance portion and the near portion, that the curvature of one or both surfaces continuously change from the distance portion to the near portion.
The surfaces of spectacle lenses are usually characterized by the so-called principal radii of curvature R
1
and R
2
at every point on the surface. (Sometimes also the so-called principal curvatures K
1
=1/R
1
and K
2
=1/R
2
are given instead of the principal radii of curvature.) Together with the refractive index n of the glass material, the principal radii of curvature govern the parameters frequently used for an ophthalmologic characterization of a surface:
Surface power=0.5·(
n
−1)·(1
/R
1
+1/R
2
)
Surface astigmatism=(
n
—1)·(1
/R
1
−1
/R
2
).
Surface power is the parameter via which an increase of power from the distance portion to the near portion is achieved. Surface astigmatism (more clearly termed cylinder power) is a “troublesome property”, because an astigmatism—inasmuch as an eye does not have an innate astigmatism to be corrected—which exceeds a value of about 0.5 dpt results in an indistinctly perceived image on the retina.
BACKGROUND OF THE INVENTION
Although any change of the curvature of the surface which is needed to achieve a surface power increase without vision being “disturbed” by surface astigmatism can be attained relatively simply along a (plane or winding) line, considerable “intersections” of surfaces will result alongside this line, leading to a large surface astigmatism which more or less impairs the lens in regions alongside the mentioned line.
On a surface having a surface power increasing from the distance portion to the near portion it is therefore not possible for reasons of surface theory to “maintain” the regions alongside a line (that is free from astigmatism or exhibits a predetermined astigmatism) free from physiologically disturbing surface astigmatism (Minkwitz Law).
Because the curvature in the distance portion must not change, it is relatively simple to design the distance portion of the progressive surface in such manner that the distance portion has a very small surface astigmatism (<0.5 dpt) or even a surface astigmatism value of “0” within a large region. On the other hand, the “quality” of the shaping of the regions lateral to the transition region is of decisive importance for the acceptability of the spectacle lens to the spectacle wearer concerned.
The basic object in designing every progressive spectacle lens is therefore to shape the lateral regions within the transition zone, and also the lateral regions of the near portion if necessary, so that the spectacle lens will be as acceptable as possible to the spectacle wearer—without any unacceptable impairment of the distance portion.
In order to achieve this basic object, the designing of a progressive spectacle lens surface contributing to power change has in the past started out from a line lying or winding in a plane—also designated as a principal meridian or a principal line—as a “backbone for the design of the surface”. This line runs centrally along the surface from top to bottom, and its course approximately follows the points of penetration of the rays of sight through the spectacle lens surface during a movement, in particular a lowering, of the glance. The principal curvatures at each point on this line were chosen in such manner that the desired increase of surface power (also designated as addition power) from the distance portion to the near portion is achieved. Starting out from this line, the lateral regions of the surface were then (more or less) suitably computed.
For the shaping of the lateral regions a number of solutions have become known. During the early days of the computation of progressive spectacle lenses a purely surface-theoretical optimization of exclusively the progressive surface was performed, in which the foremost concern was that of substantially reducing as far as possible the disturbing surface astigmatism, or “displacing” the surface astigmatism into the lateral lower regions of the spectacle lens.
Typical of this manner of proceeding are the progressive surfaces for spectacle lenses known from U.S. Pat. No. 2,878,721 or DE-AS 20 44 639, in which—provided that the progressive surface is the front surface—the curvatures of intersections of the progressive surface with plane surfaces which extend horizontally (horizontal meridians) or are perpendicular to the principal meridian (orthogonal meridians) are conic sections or curves of higher order, the curvatures of which increase in the distance portion and decrease in the near portion. The transition between the increase of curvature of the meridians in the distance portion and the decrease in the near portion occurs in the progressive zone.
This manner of proceeding results in the power difference and therewith also the surface intersections being reduced in the lateral regions. However, it is of disadvantage that because of the reduction of the power difference in the lateral regions, it becomes difficult to achieve an oriented view through the edge region and—depending on the design—very disturbing swaying sensations are experienced when looking through the lateral regions. Furthermore, the surface power along horizontal meridians changes relatively strongly.
For this reason it was proposed in DE-Patent 28 14 936 that the curvature in the distance portion or in the near portion be allowed to decrease or increase only in a strip on both sides of the principal meridian, and that the change of curvature be reversed outside this strip.
However, common to all of these approaches is a purely surface-related optimization of the progressive surface. This purely surface-related approach can be found also in more recent patent publications, such as DE-C-42 38 067 or DE-C-43 42 234.
In the last-mentioned publication an approach is described in which certain conditions for the gradient of the surface astigmatism and the surface power must be maintained. Irrespective of the circumstance that these gradients are not at all defined, for example when the surface is described by means of cubic splines, this purely surface-related optimization also disregards certain physiological requirements.
Approaches made to optimize the progressive surface in a wearing position are described in EP-A-677 177, U.S. Pat. No. 4,606,622 and DE 196 12 284.
For computing a progressive surface in the wearing position, a wearing situation is established. This relates either to a particular user for whom the individual
Altheimer Helmut
Awrath Norbert
Baumbach Peter
Brosig Jochen
Dorsch Rainer
Collins Darryl J.
Optische Werke G. Rodenstock
Sugarman Scott J.
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